Nanotechnology Spotlight

Nanocomposites from silica and spider silk

(Nanowerk Spotlight) Researchers combined two different materials from nature, both of which have unique and important properties, into one material system via genetic engineering. By combining the features of silk with biosilica through the design, synthesis, and characterization of a novel family of chimeric proteins an innovative biomimetic nanocomposite was fabricated.

Silica is widespread in biological systems and serves different functions. Biosilica skeletons found in nature are based on nanoscale composites wherein the organic components, usually proteins, are functional parts of the skeletal structures while also serving as silica-forming components. As a result, materials’ toughness is improved, strength is retained, and fine morphological control is achieved, all hallmark attributes of biological composites.

Controlled synthesis of bioinspired silica composites in vitro for novel materials design is a big challenge for researchers and materials engineers.

Researchers at Tufts University in the U.S. and Nottingham Trent University in the UK developed a novel biomimetic nanocomposite approach to synthesize silica composites using fusion (chimeric) proteins.

Professor David Kaplan, Chair of the Department of Biomedical Engineering and Director of the Bioengineering & Biotechnology Center at Tufts University, explained his group's recent research to Nanowerk:

"In our designs we exploit two critical lessons in materials science and engineering from nature: 1) nanoscale structural protein materials are used to optimize mechanical function and materials stability, and 2) improved materials properties are gained through the control of nanoscale organic–inorganic interfaces and composite structural features."

Fusion proteins have found applications in a wide spectrum of areas such as the biomedical field (they are used in immunology, cancer research, and drug delivery) and materials science (self-assembled materials such as gels, quantum dot bioconjugates, sensors, and inorganic materials synthesis).

"In our recent paper ("Novel nanocomposites from spider silk–silica fusion (chimeric) proteins") we describe new silica-based nanocomposites formed from bioengineered fusion proteins that consist of two components, and we propose a model for silk protein assembly into films and fibers and silica deposition onto the materials during the mineralization reactions" says Kaplan.

Schematic representation of the design of fusion proteins and their use in controlled silica nanocomposite formation. (A) Scheme of chimeric design with two functional domains: silk and R5. (B) Model of spider silk protein processing into films and fibers and silicification reactions on the assembled materials. (Source: PNAS, National Academy of Sciences)

Silks are intriguing biologically derived proteins that form into fibers with remarkable mechanical properties. Kaplan and his colleagues exploited the properties of silk to generate self-assembled composites in the form of films and fibers.

Kaplan is quite enthusiastic about these experiments: "The protein biomaterial self-assembling nanodomains used in our designs are genetically tailorable in terms of size, chemistry, and morphology, such that our approach offers a new platform for in situ silica formation with unprecedented control in composite materials design and properties. This approach to nanoscale material composite systems engineering, we believe, will generate new families of biomaterials that can be either preassembled in vitro or organized (selfassembled) in vivo."

With regard to potential applications, Kaplan sees several possibilities; "We see a number of options - one is new types of nanocomposites for hard tissue repair - such as bone and teeth. A second is in all green chemistry nanocomposite systems as the process we describe is all carried out in water under ambient conditions. Going forward, we would like to conduct tissue repair studies with these systems as well as broaden the types of nanocomposite materials that can be made - both in terms of composition and morphology."